1. Field of the Invention
The present invention relates to a process for manufacturing an inorganic material-based article consisting of or composed mainly of inorganic material-based fine fibers, and an inorganic material-based article which may be prepared by the above-mentioned process and consists of or is composed mainly of inorganic material-based ultra-fine long fibers.
2. Description of the Related Art
For example, an inorganic material-based sheet composed of inorganic material-based short fibers, such as glass short fibers, is favorably used as a filter or a separator in a lead accumulator, because of excellent filtering and separating properties.
The inorganic material-based short-fibers sheet was prepared, for example, by forming a sheet from material-based short-fibers in accordance with a wed-laid method. There is a possibility that some inorganic material-based short-fibers are dropped from the inorganic material-based short-fibers sheet prepared by the above-mentioned process. Therefore, it is preferable to bond inorganic material-based short-fibers by an adhesive. When the adhesive is used, however, there were disadvantages in that the adhesive is eluted, or applications of the inorganic material-based short-fibers sheet was limited.
For example, Sumio Sakka, xe2x80x9cZoru-Geru Hou no Kagaku (Science of a sol-gel method)xe2x80x9d published by Agune-Shofu, Jul. 5, 1988, discloses that short fibers having a diameter of 10 xcexcm and a length of at most 20 mm can be prepared (pages 78-79). Nevertheless, there is a possibility that some short fibers are dropped from a fiber sheet prepared from such short fibers, because of shortness, and if an adhesive is used, there were disadvantages in that the adhesive is eluted, or applications of the inorganic material-based short-fibers sheet was limited.
For example, when the inorganic material-based short-fibers sheet is used as a filter in a clean room, eluted substances may be adhered to a surface of a silicon wafer or a glass substrate. In some cases, the inorganic material-based short-fibers sheet cannot be used as a heat-resistant filter, because an adhesive is not heat-resistant.
Furthermore, the inorganic material-based short-fibers in prior art have a large diameter, and do not have pliability. Therefore, a shape of the article of the inorganic material-based short-fibers is limited to a sheet or a plate, and the application is also limited.
Recently, miniaturization and high performance of a semiconductor or an electronic component such as a circuit board mounted on a computer is desired due to the miniaturization and high performance of industrial or personal electronic equipment. For the miniaturization of the electronic component, it is important to thin the circuit board and to make wiring denser. Therefore, the material for the circuit board is required to have a reliable insulation quality enabling a thinning of line pitches, and a laser workability enabling the miniaturization of holes.
Hitherto, a glass-epoxy circuit board prepared by impregnating a substrate of a glass fibers woven fabric or a glass fibers nonwoven fabric with an epoxy resin was widely used as a circuit board carrying electronic components. Nevertheless, the glass-epoxy circuit board has disadvantages that, when holes are produced by a laser, a shape of the produced hole may not be accurate, or a fuzzing may occur.
Recently, a circuit board of organic fibers such as an aramid fiber attracted attention because of an excellent resistance to thermal expansion and a laser workability. Nevertheless, an aramide fiber has a high hygroscopity, and disadvantageously, the circuit board lacks reliable insulation quality.
Accordingly, the object of the present invention is to remedy the disadvantages in prior art and provide a process for manufacturing an inorganic material-based article which can avoid an adhesive and remedy the disadvantages caused by the adhesive used in prior art.
Another object of the present invention is to provide an inorganic material-based article having an excellent pliability from which fibers are hardly dropped, or pollutants derived from an adhesive are hardly released.
Still another object of the present invention is to provide a circuit board having an excellent reliable insulation quality and a laser workability, and sufficiently meeting the recent requirement for the miniaturization and high performance.
Still another object of the present invention is to provide a substrate for the circuit board.
Other objects and advantages of the present invention will be apparent from the following description.
In accordance with the present invention, there is provided a process for manufacturing an inorganic material-based article comprising the steps of
(1) forming a sol solution mainly composed of an inorganic component [hereinafter sometimes referred to a sol solution forming step],
(2) producing inorganic material-based gel fine fibers by extruding the resulting sol solution from a nozzle, and at the same time, applying an electrical field to the extruded sol solution to thin the extruded sol solution, and then, collecting inorganic material-based gel fine fibers on a support [hereinafter sometimes referred to a collecting step], and then,
(3) drying the collected inorganic material-based gel fine fibers to produce inorganic material-based article containing inorganic material-based dried gel fine fibers [hereinafter sometimes referred to a drying step], and/or
(4) sintering the collected inorganic material-based gel fine fibers or the inorganic material-based article containing inorganic material-based dried gel fine fibers to produce inorganic material-based article containing inorganic material-based sintered fine fibers [hereinafter sometimes referred to a sintering step].
According to the manufacturing process of the present invention, the inorganic material-based article can be prepared by the drying and/or sintering without an adhesive, and therefore, the disadvantages caused by the adhesive can be avoided.
According to a preferable embodiment of the manufacturing process of the present invention, the support used in the collecting step (2) has a three-dimensional structure. The resulting inorganic material-based article has a three-dimensional structure, and can be applied to various fields.
In accordance with the present invention, there is also provided an inorganic material-based article comprising inorganic material-based ultra-fine long fibers having an average fiber diameter of 2 xcexcm or less, and composed mainly of an inorganic component.
As above, the inorganic material-based article according to the present invention comprises long fibers, and thus the fibers are hardly dropped therefrom. Further, a diameter of the fiber is as small as 2 xcexcm or less, and the article has an excellent pliability, may have various shapes, and can be applied to various fields.
According to a preferable embodiment of the inorganic material-based article, contacting surfaces of the inorganic material-based ultra-fine long fibers are bonded to each other not via an adhesive, i.e., without an adhesive. In a preferable embodiment, the inorganic material-based article does not substantially contain an adhesive. Therefore, the article will hardly release pollutants.
According to another preferable embodiment of the inorganic material-based article, a CV value of the inorganic material-based ultra-fine long fiber in the inorganic material-based article is 0.8 or less. The inorganic material-based article composed of the inorganic material-based ultra-fine long fibers having a CV value of 0.8 or less has uniform properties.
In accordance with the present invention, there is also provided a substrate for a circuit board, comprising a fiber sheet containing inorganic material-based ultra-fine fibers having an average fiber diameter of 2 xcexcm or less, and composed mainly of an inorganic component.
A glass fiber in a glass woven fabric or a glass nonwoven fabric used in a conventional substrate for a circuit board has a thick diameter, in view of stability upon spinning or workability. The lower limitation is as large as about 5 xcexcm. Therefore, when a laser processing is carried out, the shape of the hole cannot be accurately controlled, or fuzzing may occur. On the contrary, the present substrate for a circuit board is formed from the inorganic material-based ultra-fine fibers having an average fiber diameter of 2 xcexcm or less, and thus a laser processing can be carried out without encountering the problems of the control of the shape of the hole or fuzzing. The present substrate provides workability as a substrate made of organic fibers in a laser processing. Further, the inorganic material-based ultra-fine fibers are composed mainly of the inorganic component, and the present substrate for a circuit board has a highly reliable insulation quality.
According to a preferable embodiment of the present substrate for a circuit board, a silica component contained in the material-based ultra-fine fiber is 50 mass % or more. Therefore, various glass compositions from, for example, a conventional E glass composition to a conventional Q glass (silica glass) composition may be selected dependently of various applications of the circuit board. Particularly, when the silica glass composition is used, a circuit board having a dielectric constant suitable for a high-frequency and a low dielectric dissipation factor can be manufactured.
According to another preferable embodiment of the present substrate for a circuit board, the fiber sheet has a structure of a nonwoven fabric. A structure of a glass woven fabric inevitably includes crossing portions of glass yarns. The crossing portions affect smoothness. Further, an apparent density is high, and a matrix resin is difficult to penetrate. On the contrary, the present substrate for a circuit board has the structure of a nonwoven fabric, and thus has an excellent smoothness and an excellent permeability of a resin.
According to still another preferable embodiment of the present substrate for a circuit board, the fiber sheet consists essentially of the inorganic material-based ultra-fine fibers, that is, does not substantially contain any component other than the inorganic material-based ultra-fine fibers. A conventional glass nonwoven fabric contains an adhesive, and a formation of a coating of the resin causes a poor penetration of a matrix resin into a substrate for a circuit board. On the contrary, the present substrate for a circuit board can provide a good penetration, and does not elute pollutants from an adhesive. Therefore, a circuit board having an excellent insulating property can be manufactured.
According to still another preferable embodiment of the present substrate for a circuit board, the inorganic material-based ultra-fine fibers consist essentially of long fibers. Therefore, the fuzzing may be reduced in a step of impregnating with a matrix resin or a step of processing a circuit board.
According to still another preferable embodiment of the present substrate for a circuit board, a thickness of the substrate is 80 xcexcm or less. Therefore, a thickness of a circuit board can be lowered, and the miniaturization of a space for a circuit board can be realized.
In accordance with the present invention, there is also provided a circuit board containing the above-mentioned substrate. The present circuit board has excellent properties as mentioned above.